This book project deals with the history of the various relationships which existed between the Florentine Republic and the Kingdom of Hungary during the reign of Sigismund of Luxemburg (1387-1437). This period in Florence corresponds to the epoch of the oligarchic regime, dated between the ciompi revolt (1378) and the return of Cosimo de'Medici (1434) and marked by three major censuses of the city (1378, 1427, 1433). I argue that overlaps of social networks in everyday life as well as in public sphere played a crucial part in relationships of any kind which developed between the two states. In republican Florence social networks of kin, neighbours and friends provided a solid base for human interactions at various levels, including diplomacy, geographical mobility, merchant networks and cultural exchanges. The project therefore has a strong interdisciplinary character and combines elements of quantitative research with qualitative analysis. I believe that this work may challenge our vision of complex social networks in medieval societies as well as that of the importance of various relations between these two parts of late medieval Europe.